This invention relates to the catalytic dimerization, codimerization and oligomerization of olefins.
It has as its object a catalytic formula that results from the dissolution of a nickel complex that contains at least one heterocyclic carbene ligand with at least one hydrocarbylaluminum halide and optionally at least one organic solvent. This invention also has as its object the use of this catalytic composition in processes of dimerization, codimerization and/or oligomerization of olefins.
It is known to prepare catalysts for dimerization or codimerization of monoolefins such as ethylene, propylene, butenes or pentenes. Among these catalysts, it is possible to cite in particular by way of examples: the products for interaction of xcfx80-allyl nickel phosphine halides with Lewis acids (French Patent FR-B-1 410 430), the products for interaction of nickel phosphine halides with Lewis acids (U.S. Pat. No. 3,485,881) and the products for interaction of certain nickel carboxylates with hydrocarbylaluminum halides (U.S. Pat. No. 3,321,546).
Nearly all of these catalysts use a ligand such as an organic phosphorus compound. It is preferable, however, to be able to use phosphorus-free oligomerization catalysts. It would be possible to use catalysts in which nickel is deposited on a mineral substrate that comprises acid sites, such as silica, alumina or silica-aluminas. These are solid catalysts, however, unlike catalysts in the liquid phase of the invention.
Some organometallic nickel complexes that contain heterocyclic carbene ligands have been described in the prior art (International Application WO-A-99/06 004, U.S. Pat. No. 5,728, 839 and Patent Application EP-A-0 798 041). Such complexes have the advantage of being very stable. More particularly, these monocarbene or bicarbene ligands lead to nickel complexes that are thermally and chemically stable primarily with regard to oxidation. These carbene ligands were the object of a survey in Angew. Chem. Int. Ed. Engl. 1997, 36, 2162. These are "sgr"-donor ligands and xcfx80-acceptor ligands that form very stable bonds with transition metals. Their electronic properties can be compared to those of basic trialkylphosphines.
It has now been found that bringing into contact
a nickel complex that carries at least one monocarbene or bicarbene ligand that corresponds to, for example, Formulas (I) and (II) that are provided below;
with at least one hydrocarbylaluminum halide;
and optionally an organic solvent led to an active system for dimerization, codimerization and/or oligomerization of olefins. 
The nickel compounds that are used according to the invention are salts of nickel or organometallic compounds that may or may not be charged and that correspond to the general formula (already described in Patent Application EP-A-0 798 041):
(NiaXbYdLc)n(A)n
in which:
a, b, c, d and n are integers with a equal to 1, 2 or 3; b equal to 0 to 2xc3x97a; d equal to 0 to 2xc3x97a; c equal to 1 to 4xc3x97b; n equal to 0, 1 or 2;
X and Y, identical or different, each represent a mono- or poly-dentate ligand that may or may not be charged; by way of examples, it is possible to cite halides, carboxylates (for example ethyl-2-hexanoate), acetylacetonate, sulfate, phenolates, mono- and di-olefins, xcfx80-aromatic compounds, alkyl or aryl radicals, phosphines, phosphates and carbon monoxide;
L is a heterocyclic mono- or di-carbene that corresponds to, for example, one of general formulas (I) and (II) above, in which R1, R2, R3, R4, R5 and R6, identical or different, each represent hydrogen, a hydrocarbon-containing group, aliphatic group, saturated or unsaturated group, or aromatic group that comprises 1 to 12 carbon atoms, and Q represents an aliphatic divalent radical with 1 to 4 carbon atoms;
A is a sparingly coordinating anion; by way of examples, it is possible to cite tetrafluoroborate anions, hexafluorophosphate anions, tetraphenylborate anions and derivatives thereof, tetrachloroaluminate anions, hexafluoroantimonate anions, trifluoroacetate anions, trifluoromethylsulfonate anions and acetate anions.
Heterocyclic carbenes L can be generated from corresponding imidazolium or bis(azolium) salts by deprotonation. The transition metal can play the role of reducing agent.
By way of nonlimiting examples of heterocyclic mono- or bicarbene ligands, the carbene ligands that are described by formulas (1), (2) and (3) that are given below will be cited. 
By way of nonlimiting examples of nickel compounds that can be used according to the invention, it is possible to cite the complexes of NiCl2, [dimethyl-1,3-imidazolylidene-2]2; NiI2, [dimethyl-1,3-imidazolylidene-2]2; xcfx80-allyl nickel chloride (dimethyl-1,3-imidazolylidene-2) ; NiCl2, [dimethyl-1,1xe2x80x2-imidazole-diylidene-2,2xe2x80x2-methylene-3,3xe2x80x2]2 and NiCl2, [dimethyl-1,1xe2x80x2-imidazole-diylidene-2,2xe2x80x2-ethylene-3,3xe2x80x2]2, NiI2[dimethyl-1,1xe2x80x2-imidazole-diylidene-2,2xe2x80x2-methylene-3,3xe2x80x2]2 and NiI2, [dimethyl-1,1xe2x80x2-imidazole-diylidene-2,2xe2x80x2-ethylene-3,3xe2x80x2]2.
The hydrocarbylaluminum halide derivatives that are used according to the invention have as a general formula AlRXX3xe2x88x92x, in which R is a hydrocarbon-containing radical comprising 1 to 12 carbon atoms, which can be alkyl, linear or branched, cycloalkyl, aryl or aralkyl, whereby X is chlorine or bromine and x is a number from 1 to 3. By way of nonlimiting examples of these derivatives, it is possible to cite isobutylaluminum sesquichloride, ethylaluminum sesquichloride, dichloroisobutylaluminum, dichloroethylaluminum and chlorodiethylaluminum.
The components of the catalytic formula can be mixed in any order.
The optional solvent that makes it possible to carry out the mixing of the components of the catalytic formula and in which the catalysis can be carried out is a hydrocarbon-containing solvent, for example an alkane or an aromatic hydrocarbon, or else a halogenated hydrocarbon or else the mixture of olefins that is produced in the oligomerization reaction.
The molar ratio of the organic aluminum compound to the nickel compound, expressed by the Al/Ni ratio, is, for example, from 2/1 to 50/1 and preferably 2/1 to 20/1.
The olefins that can be dimerized, codimerized or oligomerized by the catalytic compositions according to the invention are ethylene, propylene, n-butenes and n-pentenes, alone or in a mixture, pure or diluted by one or more alkane(s), such as are found in xe2x80x9cfractionsxe2x80x9d that are obtained from petroleum refining processes, such as catalytic cracking or steam-cracking.
The catalytic reaction of dimerization, oligomerization or codimerization of olefins, which is also an object of the invention, can be conducted in a closed system, in a semi-open system or continuously with one or more reaction stages. The reaction temperature can be xe2x88x9240 to +80xc2x0 C., preferably xe2x88x9220 to +50xc2x0 C., under pressure conditions such that the reagents are kept at least for the most part in liquid phase or condensed phase. The heat that is produced by the reaction can be eliminated by all of the means that are known to one skilled in the art.
The process can be used in a reactor with one or more reaction stages in series, whereby the preconditioned olefinic feedstock and/or the catalytic composition is introduced continuously or in the first stage or in the first and any other of the stages. At the outlet of the reactor, the catalyst can be deactivated, for example by injection of ammonia and/or an aqueous solution of soda and/or an aqueous solution of sulfuric acid. The unconverted olefins and the alkanes that are optionally present in the feedstock are then separated from the oligomers by distillation.
The products of this process can find an application, for example, as components of fuels for automobiles and/or as feedstocks in a hydroformylation process for the synthesis of aldehydes and alcohols.